Inks having low rub-off properties have been known in the prior art. Such inks typically contain waxes of various types and the resultant inks will exhibit improved mar-resistance, slip properties. Wax of a controlled fine particle size can be mixed or ground into the batch along with pigments or may be introduced during the final blending operations. Alternatively, the wax may be compounded into a “wax media” by dispersing or melting the wax into the varnishes and/or solvents and adding these to the ink.
It is also well-known that the non-rub qualities imparted by an individual wax are a function of both the particle size and the hardness as well as the melting temperature of the particular wax that is being used. However, addition of waxes to inks in order to solve the rub-off problem introduces other problems. First, on a scale of 100 representing no rub-off, waxes added to inks will result in reduction in rub-off to a level of only about 60. Second, with the heat and movement imparted by the friction of constant rubbing under pressure, particles of the ink film can ball up and mark unprinted areas. Additionally, the more waxes that are added to improve rub resistance, the more problems are introduced in respect to gloss and hardness characteristics. Addition of waxes to inks almost invariably decreases their gloss. Accordingly, a compromise must be achieved between the desired level of non-rub properties and gloss. Finally, there is the factor of increased cost associated with the ink containing relatively expensive waxes such as microcrystalline waxes and polytetrafluoroethylene powder. In the case of news inks, cost is an extremely important factor and, therefore, at the present time news inks do not ordinarily contain any waxes; furthermore, waxes provide only minimal reduction of rub-off in news ink formulations.
Synthetic waxes such as polyethylene waxes and polytetrafluoroethylene powders are now the most popular materials used in the ink industry. Such materials are usually added in the form of “non-rub” or “slip” media which are fine dispersions of the material in the solvents, oils and resins, etc., of the particular type of ink formulation in which it is to be incorporated. Additives prepared from polytetrafluoroethylene powders are suitable for all types of printing inks, but are especially ideal for heatset inks, where the temperature of the drying apparatus does not cause them to soften or melt. Polytetrafluoroethylene-based powders can also be stirred into finished inks to improve their rub and scuff resistance. Nevertheless, the relative cost of a polytetrafluoroethylene powder is prohibitively high for many-applications, e.g. news inks.
It is also known, that printing ink incorporates several different raw materials to formulate the finished ink. Such raw materials are dry pigment, pigment flushes, resins, oils, and specialty surface treated additives. Basically, these raw materials are petroleum based. Newspaper, magazine, fliers, board packaging and the like are all printed using large quantities, i.e., hundreds of thousands of pounds, of these ink ingredients yearly. The equipment used in the printing process is often computerized allowing for high speeds. It is essential that the raw materials meet and sometimes exceed quality control expectations. Melting points, particle size distribution, color, viscosities, tack, and flow properties all play a role in producing a finished ink.
Historically, the printing ink industry has utilized ink additives which are comprised of varying combinations of raw materials such as resins, ink solvents, polytetrafluoroethylene powders, microcrystalline, polyethylene and paraffinic waxes. Typical additives are classified as heat set additives, sheet-fed additives and UV ink additives. Due to the volatility of the resinous vehicles, safety precautions and proper explosion proof equipment is necessary to handle the possible hazards associated with these types of materials.
The heat set additives are typically comprised of a resin vehicle/carrier with a viscosity of 50,000-100,000 centipoise such as phenolic, hydrocarbon, anhydrous and other such family of resins, in addition to MagieSol 47 Oil (ink solvents), and a micronized polytetrafluorethylene for slip resistance. Typically the 47 or 470 solvents are used in heat set applications as well as ultra-violet inks. These types of solvents are necessary to achieve the desired wetting conditions required for creating the resin solution. The resins are used for rub and gloss resistance. The micronized polytetrafluoroethylene typically has a mean particle size of 3-5 microns. This is necessary for slip resistance (low coefficient of friction).
The solvent mixture is used as a vehicle/carrier for the polytetrafluoroethylene to protect the ink film. Typically, the range of the polytetrafluoroethylene loading level is 50-70% into the resin vehicle. The vehicle is formed when the resin reacts with the ink solvent. This is accomplished in a jacketed mixing vessel when the solid resin is heated to 10 degrees above the resins melt point, clarity is achieved and then slow cooled to ambient to make a resinous liquid. Viscosity ranges of the liquid at ambient typically are between 50,000-100,000 centipoise. Once this reaction is completed, 50-70% polytetrafluoroethylene is added to make a finished dispersion which is able to be added to the ink at about a 4% loading. This product would be added to the heat set ink and printed on a substrate. Direct heat cures the ink film. This causes the additive to rise to the surface of the ink causing a protective coating to form over the ink on the substrate. This restricts the amount of ink transference such as in the case of a newspaper where the ink rubs off onto the hand. Precautions should be taken when heating as the ink solvents volatilize into the atmosphere. In order to test the effectiveness of the rub resistance of the ink on the substrate, a Sutherland Rub Tester is used with a 4 lb. weight by 50 strokes. This measures the amount of ink being transferred from the substrate. This testing mimics the friction caused when finished products such as magazines, labeling on cans and packaging, etc. are transported to their end destination for the consumer.
The polytetrafluoroethylene resin solvent product used for sheet fed inks is not inter-changeable with heat set. Sheet fed inks are dried by oxidation as opposed to heat set which requires direct heat. The preferred performance additive here is typically polyethylene, microcrystalline or paraffinic type waxes into a solvent carrier. For added slip resistance, a low percentage of polytetrafluoroethylene (typically 5-10%) may be added to the composition.
The sheet fed inks have curing accelerators which react with the atmosphere causing a slow curing of the ink film. Historically, sheet fed ink is cured after 12-24 hours as opposed to the heat set inks which are cured immediately after exposure to direct heat. The additives in the sheet fed ink systems are comprised of a polyethylene or paraffinic waxes in a solvent carrier such as MagieSol 52 and must be produced using a heat exchanger. The procedure would be to add the polymer with the ink solvent in a jacketed enclosed explosion proof mixing vessel followed by heating to about 10 degrees above melting point of wax or polymer. Once clarity is achieved and polymer is completely melted, dry micronized polytetrafluoroethylene powder may be added if desired. Once totally dissolved, the temperature is reduced to between 120-140° Fahrenheit. The material is pumped from the vessel into a jacketed heat exchanger which causes the product to be quick cooled and produces the desired particle size needed. The discharge temperature of the solution should be 100 degrees F or below to achieve the desired viscosity. This is necessary to provide a particle size distribution between 3-5 microns and create enough surface area to meet with the expectations of the sheet fed ink and to create a broad surface area to maintain a high viscosity to encompass the wax additive so that it stays in suspension. This is known as a compound with a viscosity range of 100,000-500,000 centipoise. Once this additive is incorporated into sheet fed ink, the wax particles will work in conjunction with the accelerators in the sheet fed ink to bring them to the surface as a protective coating. As the sheet fed is cured, the solvent is released into the atmosphere. Once the ink is cured, the same procedures used in the previously described heat set evaluations are utilized with the Sutherland Rub Tester.
Ultraviolet inks also referred to as UV inks are cured using ultraviolet rays. Typically with UV film, microcrystalline and paraffinic waxes cannot be used due to the volatility of the reaction under ultraviolet which causes a cratoring or swelling of the ink film. Typically a polyethylene compound or a polytetrafluoroethylene dispersion or a polyethylene/polytetrafluoroethylene compound is used here instead. Once the ink film is cured under UV, the Sutherland Rub Testing is used for evaluation as is used in the previously described heat set and sheet fed ink systems.
As it will be appreciated, there are three distinctive products that must be utilized for each individual application. Also, powders such as polytetrafluoroethylene, polyethylene, and Fischer-Tropsch powders that must be micronized at a low micron mean particle size of 3-4 microns to maintain the ink specifications are used but not preferred due to handling problems such as dusting and as in the case of polytetrafluoroethylene, risk of Teflon fever which can occur when powder gets onto skin and into the saliva membranes. Many precautions must be taken when using these micronized powders in manufacturing such as installing pneumatic powdered transfer systems, clean rooms and ventilation systems along with OSHA regulated guidelines for personnel. Because of the many variables that arise with these ink film systems, typically high percentages of waxes and polytetrafluoroethylene powders are incorporated into these vehicles/carriers to protect the ink film.
Additionally, there have been problems with petroleum supplies worldwide. Some of the problems are high out-of-control pricing, land fill, environmental issues, supply and demand etc. In order to address these concerns, the ink manufacturers initiated efforts to develop inks with vehicles based on biodegradable derived materials to reduce the industry's dependency on petroleum. Thus there is a long felt need for biodegradable surface treated additives.
Some previous efforts to replace petroleum-derived components in printing inks include the following patents. U.S. Pat. No. 5,122,188 to Erhan, et al. discloses the use of “heat bodied” vegetable oils as a vehicle. The patent teaches that it is believed that “heat bodying” promotes polymerization of the oils utilizing double bonds thereby increasing the viscosity of the oil to desired range of between about 1.6-18 poises.
U.S. Pat. No. 5,552,467 to Reiter, et al. relates to a thermosetting lithographic ink compounded from solid resin, drying oil alkyds, bodied drying oil, vegetable oil, fatty acids, multifunctional unsaturated polyester, reducing agent and transition metal salts of organic acids, multifunctional unsaturated polyester, reducing agent and transition metal salts of organic acids. The patent teaches that the lithographic ink solution includes hydroperoxides of peroxides to promote free radical polymerization of the ink when activated by heating.
U.S. Pat. No. 6,762,216 to Fukuda, et al. teaches a printing ink composition that includes a vegetable oil, and a rosin-modified phenol resin having a weight average molecular weight of at least 30,000 dissolved in a vegetable oil. The ink composition further includes a volatile organic solvent up to about 3% by weight. The patent teaches that the vegetable oil is the main component for dissolving the resin in the ink, thereby reducing the volatile organic solvent below that used in conventional inks.
U.S. Pat. Application Publication No. 2005/0131103 to Hassan, et al. teaches waxes prepared from hydrogenated plant oils, which are formulated into aqueous ink and paper coating compositions. The waxes disclosed in this application are proposed as substitutes for petroleum based compositions and are useful in aqueous based ink formulations.
U.S. Pat. No. 5,591,796, issued to Wisniewski et al, discloses the use of polytetrafluroethylene in combination with poly-alphaolefins and suspended with resins in petroleum distillates as pumpable friction—reducing additives
U.S. Pat. No. 5,749,949 to Tavares teaches the use of sintered polytetrafluoroethylene with resins suspended in petroleum distillates as friction reducers for inks.
U.S. Pat. No. 6,409,811 B1 to Tavares, et al, further describes the use of sintered polytetrafluoroethylene, but this time with petrolatum, microcrystalline waxes as friction reducers.